1. Field of the Invention
The present invention relates to a method and related devices used to regenerate cartilage in articulating joints.
2. Description of the Prior Art
The skeleton has specialized joints for different types of movement. Joints have two or more bones that articulate with respect to each other. Joints extend and flex as hinges like the fingers. They rotate like the ball within the socket of the hip.
The bones of a healthy joint are not actually seated against one another during movement. A layer of articular cartilage usually separates joint bones. Articular cartilage decreases the stress on the bones during motion and subsequently the wear and tear of the bone over a lifetime of movement.
Both friction and compression are often present during movement. Walking upright, for example, places both compressive and frictional stress on the hip. The weight of the upper body pushes down on the joint while the leg rotates within the hip.
Frictional stress is due to the relative movement of two objects. In this case, bone moving against bone generates a great deal more frictional stress than is the case when articular cartilage is present. Without articular cartilage, the surfaces of the bones are exposed, friction increases and movement becomes more difficult. If the bone is covered with cartilage, the bones smoothly glide on the cartilage and movement is easier. By reducing friction, articular cartilage eases movement.
Bones of the joint are not only stressed by movement and friction. Articular cartilage cushions bones against compression. Compressive stress compresses bones by the pressure of bone against bone, such as the weight of the body pushing against the bone or the force of one bone pushing against another.
Disease and injury damage articular cartilage. Osteoarthritis, chondromalacia and rheumatoid arthritis erode the cartilage from the joint. Injuries such as bone fractures can tear or bruise the cartilage, which can also lead to cartilage loss.
The loss of articular cartilage increases friction and compression during movement. The remaining articular cartilage rapidly degenerates under these stresses which causes the bones of the joints to touch against one another directly. The movement of exposed bone against bone further degenerates the articulating surfaces of the bones in the joint to decrease mobility and increase pain.
Repairing damaged joints may require joint replacement. Surgical repair of the damaged joints, such as hip replacement with a prosthesis, is a major operation. Surgical replacement, especially of large joints, is painful and traumatic, often resulting in substantial blood loss and requiring a lengthy recovery period. Furthermore, surgical replacement often requires the surgeon to strip away the cartilage attached to any remaining bone to properly insert and fit the prosthesis. This leaves the joint with little if any remaining articular cartilage.
The cells of native articular cartilage do not regrow in situ. However, if the damaged cartilage is removed and the bone is wounded, such as by grinding, the joint reheals. The wounded bone serves as a source of stem cells, such as endothelial cells and other pleuripotential cells, and chondroblasts. The stem cells grow out of the wounded bone and produce a layer of cartilage. This newly grown cartilage serves to protect the joint bones from friction and compression, much like native articular cartilage does.
Alternatively, stem cells can be transplanted to the joint. These stem cells can be harvested either in vitro from cell culture or in vivo from other parts of the patient's or donor's body. In addition, growth and attachment factors can be delivered to the joint by attaching them to a scaffolding or matrix attached to the joint.
Whether from wounded bone or transplantation, fragile stem cells subjected to compressive or frictional stresses do not grow and form a layer of cartilage. The stresses placed on the growing cells at the surface are great, comparable to growing cells under a moving rock that scrapes and grinds.
The prior art does not adequately address the problems of protecting the stem cells from compressive and frictional stress. A hip replacement, for example, replaces the damaged femoral head and reams the acetabulum to fit the new femoral prosthesis. The prosthetic femoral head directly contacts and rubs against the raw acetabulum with each movement.
Prior art protective caps inadequately protect delicate stem cells. These caps provide a smoother surface which reduces friction during movement. This reduction of friction is decreased, however, whenever the bones move against any irregularity in the surface of the bone, such as peaks or valleys. Furthermore, the caps have little effect on the reduction of compression. The force of bone against bone still bears directly on the stem cells.
Therefore, there are a number of objects of the invention. One object of the invention is to shield the surface of the bone to decrease the compression and frictional stresses and aid in the regeneration of cartilage. The invention provides a protected surface for stem cells, as well as grafted cells and transplanted materials to attach and grow, such as fibroblasts, chondroblasts, fetal tissue, periosteum, cartilage and artificial cartilaginous-like materials.
Another object of the invention is to repair the joint without requiring joint replacement.
Another object of the invention is to provide access to stem cells directly from the bone.
Another object of the invention is to deliver cells and cartilage growth enhancing factors to the site. Cells can be transplanted along with any desired growth and/or attachment factors and delivered to the joint by attaching them to the shield and/or spacers of the invention. The shield and spacers can also be used to attach and maintain scaffolding material carrying transplanted cells or factors to the joint.
Still another objective of the invention is to fasten to the bone a construct such as a membrane holding gels, sponges and the like, which may be used to introduce cells and cartilage growth enhancing factors.